FIG. 26 shows a conventional DC/DC converter 8 and a conventional control device 91.
The DC/DC converter 8 shown in FIG. 26 is a depression type DC/DC converter.
FIG. 26 is an explanatory diagram showing the concern of an output voltage eo, an inductor current (iL) and an operating state of a switch SW.
The control device 91 detects the output voltage eo of the DC/DC converter 8 and the inductor current iL.
Wherein the inductor current iL is a voltage drop of a resistance rL for detecting the inductor current.
A digital detected value of output voltage eo is defined as Eo, and a digital detected value of the inductor current iL is defined as IL.
The control device 91 calculates a PID control variable based on a multiplication values (Eo*IL) of these detected values.
Specifically, the control device 91 determines a timing when the electric switch SW turns off.
An ON-time Ton of the electric switch SW is determined by the timing being determined.
And the control device 91 can control the electric switch SW via a drive circuitry 92.
In the DC/DC converter 8 shown in FIG. 26, it assumes that the output voltage eo gradually rose.
Or in the DC/DC converter 8, it assumes that the inductor current iL gradually increased.
When the output voltage eo is over a desire value eo*, the inductor current is over a desire value iL*.
The desire value iL* is a value that converted the output desire voltage eo* into a current iL.
In this case, the control device 91 controls a rise of output voltage eo by hastening an off-timing of electric switch SW.
On the other hand, in the DC/DC converter 8 shown in FIG. 26, it assumes that output voltage eo gradually fell, or a value of the inductor current iL gradually decreased.
Then it assumes that the inductor current iL was less than a desire value iL*.
As a result, inductor current iL may decrease from desired value iL*.
In this case, the control device 91 inhibits a decrease of the output voltage eo by delaying an off-timing of switch SW.